Biological hazards, also known as biohazards, refer to biological substances that pose a threat to the health of living organisms, primarily that of humans. This can include samples of a microorganism, virus or toxin (from a biological source) that can affect human health. It can also include substances harmful to other animals.

The term and its associated symbol are generally used as a warning, so that those potentially exposed to the substances will know to take precautions. The biohazard symbol was developed in 1966 by Charles Baldwin, an environmental-health engineer working for the Dow Chemical Company on the containment products.[1]

It is used in the labeling of biological materials that carry a significant health risk, including viral samples and used hypodermic needles.

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Bio hazardous agents are classified for transportation by UN number:[2]

Category A, UN 2814 – Infectious substance, affecting humans: An infectious substance in a form capable of causing permanent disability or life-threatening or fatal disease in otherwise healthy humans or animals when exposure to it occurs.

Category A, UN 2900 – Infectious substance, affecting animals (only): An infectious substance that is not in a form generally capable of causing permanent disability or life-threatening or fatal disease in otherwise healthy humans and animals when exposure to themselves occurs.

The United States Centers for Disease Control and Prevention (CDC) categorizes various diseases in levels of biohazard, Level 1 being minimum risk and Level 4 being extreme risk. Laboratories and other facilities are categorized as BSL (Biosafety Level) 1–4 or as P1 through P4 for short (Pathogen or Protection Level).

Biohazard Level 1: Bacteria and viruses including Bacillus subtilis, caninehepatitis, Escherichia coli, and varicella (chicken pox), as well as some cell cultures and non-infectious bacteria. At this level precautions against the biohazardous materials in question are minimal, most likely involving gloves and some sort of facial protection.

Biohazard Level 2: Bacteria and viruses that cause only mild disease to humans, or are difficult to contract via aerosol in a lab setting, such as hepatitis A, B, and C, some influenza A strains, Lyme disease, salmonella, mumps, measles, scrapie, dengue fever, and HIV. Routine diagnostic work with clinical specimens can be done safely at Biosafety Level 2, using Biosafety Level 2 practices and procedures. Research work (including co-cultivation, virus replication studies, or manipulations involving concentrated virus) can be done in a BSL-2 (P2) facility, using BSL-3 practices and procedures.

Biohazard Level 4: Viruses that cause severe to fatal disease in humans, and for which vaccines or other treatments are not available, such as Bolivian hemorrhagic fever, Marburg virus, Ebola virus, Lassa fever virus, Crimean–Congo hemorrhagic fever, and other hemorrhagic diseases and rishibola. Variola virus (smallpox) is an agent that is worked with at BSL-4 despite the existence of a vaccine, as it has been eradicated. When dealing with biological hazards at this level the use of a positive pressure personnel suit, with a segregated air supply, is mandatory. The entrance and exit of a Level Four biolab will contain multiple showers, a vacuum room, an ultraviolet light room, autonomous detection system, and other safety precautions designed to destroy all traces of the biohazard. Multiple airlocks are employed and are electronically secured to prevent both doors opening at the same time. All air and water service going to and coming from a Biosafety Level 4 (P4) lab will undergo similar decontamination procedures to eliminate the possibility of an accidental release. Currently there are no bacteria classified at this level.

The biohazard symbol was developed by the Dow Chemical Company in 1966 for their containment products.[1] According to Charles Baldwin,[1] an environmental-health engineer who contributed to its development: "We wanted something that was memorable but meaningless, so we could educate people as to what it means." In an article he wrote for Science in 1967,[3] the symbol was presented as the new standard for all biological hazards ("biohazards"). The article explained that over 40 symbols were drawn up by Dow artists, and all of the symbols investigated had to meet a number of criteria:

Striking in form in order to draw immediate attention;

Unique and unambiguous, in order not to be confused with symbols used for other purposes;

Quickly recognizable and easily recalled;

Symmetrical, in order to appear identical from all angles of approach;

Acceptable to groups of varying ethnic backgrounds.

The chosen symbol scored the best on nationwide testing for memorability.[4]

The design was first specified in 39 FR 23680 but was dropped in the succeeding amendment. However, various US states adopted the specification for their state code.[5]

There are four circles within the symbol, signifying the chain of infection.

Agent: The type of microorganism, that causes infection or hazardous condition.

Host: The organism in which the microorganism Infect. The new host must be susceptible.

Source: The host from which the microorganism originate. The carrier host might not show symptoms.

Transmission: The means of transmission, mostly direct or indirect. Some routes of transmission include air, insect, direct contact and contaminated surfaces.